Fatty acid methyl esters such as biodiesel are an alternative fuel source to petro-diesel, JP-8, and standard gasoline. Moreover, the use of biodiesel is growing in popularity and market penetration in the United States and worldwide. As its name implies, biodiesel is a processed fuel derived from biological sources. Indeed, biodiesel is typically a fuel comprised of fatty acid alky esters of long chain fatty acids that are derived from triglycerides, which are commonly obtained from vegetable oils and animal fats of various origins. As a general rule, biodiesel has the formula R′OOCR, where R′ is a straight chain lower alkyl (e.g., C1 to C8) and R is a hydrocarbon chain from C8 to C24.
Generally, biodiesel is produced through a transesterification reaction that occurs when a triglyceride is combined with an alcohol and a catalyst to produce fatty acid alkyl esters (biodiesel) and glycerin (which is also known as glycerin and glycerol). In this regard, a homogeneous catalyst comprising an alkali metal and having a basic pH (“alkali catalyst”), such as an alkali alkoxide or an alkali hydroxide, is often used to cause the transesterification reaction to proceed.
As described above, the transesterification reaction may produce a biodiesel and glycerin, which generally separate into two distinct phases. In this regard, some amount of the alkali catalyst and some amount of the alcohol are often dissolved in the lower glycerin phase, while trace amounts of the alkali catalyst can also be found in the upper biodiesel phase. Additionally, where free fatty acids (or fatty acids that are not bound to other molecules) are present in the reaction mixture (e.g., from being added to the reaction with the triglyceride or by being formed as the triglyceride is reacted in the transesterification reaction), the alkali catalyst causes saponification of the free fatty acids to form alkali salts of the fatty acids (“fatty acid alkali salts”). As in the case of the alkali catalyst, some amount of the fatty acid alkali salts is typically contained in the glycerin phase, while trace amounts of the fatty acid alkali salts can be found in the biodiesel phase.
In some conventional processes for producing biodiesel, strong acids are used to wash the products of the transesterification reaction to neutralize the alkali catalyst and/or to recover free fatty acids from the fatty acid alkali salts. The use of strong acids, however, is not without its shortcomings. For example, where strong acids are used to neutralize the alkali catalyst and/or to recover free fatty acids from the fatty acid alkali salts that are present in the glycerin phase, dissolved alkali salts are typically formed in the glycerin phases. In turn, these dissolved alkali salts often have to be removed through one or more additional steps before the glycerin phase can be purified. In another example of a shortcoming associated with the use of strong acids, the use of such acids can require the transportation, storage, and handling of the hazardous chemicals.
In some other conventional processes, water is used to wash the biodiesel and/or the glycerin. Such processes, however, typically result in the formation of a dissolved alkali hydroxide in the glycerin phase. As in the removal of the alkali salts (discussed above), the removal of alkali hydroxides from the glycerin phase often requires one or more additional steps for the purification of the glycerin.
Accordingly, it would be an improvement in the art to provide improved techniques to remove and recover alkali catalysts and free fatty acids from various transesterification reaction products and participants.